Turn around and climb up the rocks behind you, follow the walkway to the cave entrance furthest from you. Break the covering on the small hole and follow the passageway. In the chamber there are two exits, 1 left, 2 right (hidden behind the rock on the right);
1 go to the entrance on the left, then left again for some ammo
2 go along the passageway then left for ammo
Follow both to the right to get to the next larger chamber with a bullsquid in it and 2 more exits, 1 raised up with a small ramp leading upto it, 2 at ground level near start of small ramp;
1 then left comes to dead end with nothing
1 then right comes to health pool chamber
2 quickest route to health pool chamber
From the health pool chamber follow the passageway to some floating platforms, start from left and work your way up the platforms. Follow the tunnel onto 2 more platforms and a health pool. Stay on platform until the alien craft has blown up one of the large spikes to form bridge. (Jumping on the other two platforms and going into the cave will give some ammo, and a teleporter back to the current health pool). Cross over then break the cover on the ground to drop down the shaft.
Follow the passageway to a waterfall and drop down, jump on the boost pad to get pushed up into next water fall.
Head up river to health pool chamber then flow the river down the other passageway. Go right up 2 water falls and onto another boost pad onto the high up ledge. Follow the corridor to the teleporter relay that “Dr Rosenburg” spoke of. Use the generator then align the yellow markers with the red triangles on the control console. Head down tunnel where the ceiling will collapse, climb up the rubble then drop down to health pool. Follow passage to an open chamber, the left jump pad will take you to the small island for ammo, continue up corridor then drop down back to where you started the level and head for the teleporter back to black mesa.
“Dr Rosenburg” will advise you of needing a teleporter battery. Follow him to the "Auxiliary Generator Access" lift. Take the lift down to “Power Struggle”.